Rhesus Monkeys Took Male Birth Control And They’re Just Fine

It's another step towards creating a male contraceptive for humans.

Male birth control options are scarce right now, and don't really extend beyond condoms or vasectomy. Researchers are inching toward making them more available, at least in primates.

A new contraceptive called Vasalgel has been shown to be an effective form of birth control in rhesus monkeys in a study that lasted over one year, reported the California National Primate Research Center at the University of California, Davis. The results of the study were published this week in Basic and Clinical Andrology, while the drug itself is developed by Revolution Contraceptives LLC, a social venture subsidiary under the Parsemus Foundation.

Although it hasn't yet been tested in humans, clinical trials should start next year.

Vasalgel is a nonhormonal, long-acting, and maybe even reversible contraceptive for males. It's a polymer hydrogel, which means that it functions by blocking sperm, and it's administered with an injection into the vas deferens—the duct that carries sperm.

In the study, injecting Vasalgel into mature rhesus monkeys' vas deferens prevented contraception. "We have studied Vasalgel in animal models and found it to be well-tolerated with no discernible long-term side effects," Elaine Lissner, founder and trustee of the Parsemus Foundation, told Motherboard in an email. "In that way, it is more similar to vasectomy than to a pill."

If it were to be approved for use in humans, Vasalgel would be a one-time injection, as it was for the monkeys. The new contraceptive is meant to be a vasectomy alternative, but unlike a vasectomy, the researchers want to make it reversible, which they've shown to be possible in rabbits, Lissner said. (That research has not yet been published.)

When the human trials do start, Angela Colagross-Schouten, lead veterinarian of the study in male rhesus monkeys, predicts that the injection will be much simpler. "We have found that the rhesus macaque [monkey] vas deferens appears to be somewhat more fragile than the human vas deferens, making the placement of Vasalgel a bit more complicated," she told Motherboard in an email.

The contraceptive had no effect on the monkeys' sex drive or behavior, she added. "Once returned to their social group, males immediately began to engage in normal social behavior, including mating with females," Colagross-Schouten said.

About half of men surveyed say they would be open to using a male contraceptive, according to the Parsemus Foundation, though currently male birth control accounts for only 21 percent of contraceptive use worldwide. Women, too, would surely welcome the availability of a new form of male birth control, beyond IUDs and the pill.